The invention is a method for braking a vehicle having an adjustable hydrostatic drive unit, in which the driving engine absorbs a drag moment and the kinetic energy of the vehicle is partially reduced hydraulically when the maximum drag moment absorbable by the driving engine is exceeded. U.K. Patent Application No. 2,205,632, which is hereby incorporated by reference, discloses that a vehicle with a hydrostatic drive unit can be braked hydraulically without running the driving engine or the hydrostatic motor at an excessively high rpm because a regulator adjusts a variable displacement pump for an additional hydraulic drive toward the full delivery volume after a limiting rpm value is exceeded on the drive motor side and the delivery pressure generated is reduced by valves, to cause a reduction in the kinetic energy of the vehicle and the driving engine is simultaneously slowed, i.e., the speed is reduced.
However, this braking process is disadvantageous because when a vehicle traveling downhill is to be braked in this manner, i.e., a vehicle upon which kinetic energy is acting, in addition to the kinetic energy, the power in the hydraulic circuit is continuously converted to heat as long as the downhill travel continues and the drag moment of the vehicle is greater than that which can be absorbed by the driving engine. Under certain circumstances, the vehicle will proceed at a constant high speed, but a speed increase may be prevented by braking. However, the oil in the hydraulic circuit may be heated to a temperature that requires cooling which protects the driving engine from damage but braking of the vehicle does not occur and an additional brake must be used to stop the vehicle.
The present invention avoids the above shortcomings and provides an improved hydraulic braking method while avoiding overspeeds of the driving engine.